Some of the rolling, rural countryside of southwestern Illinois has become just a 20-minute commute from the sprawling city of St. Louis, Missouri, across the Mississippi River, now that newly built roads have opened up the landscape. But as more houses rise in rapidly developing bedroom communities, increasing levels of coliform bacteria—probably originating from septic systems and livestock—are being found in the groundwater. Trace amounts of pesticides, including atrazine, also are present.
These contaminants, in large enough quantities, can pollute groundwater and cause public health problems. They also appear to be responsible for the decreased habitat and population of a little-known cave-dwelling crustacean, the Illinois Cave Amphipod (Gammarus acherondytes), a tailless shrimp that can grow up to 20 mm in length and that swims in underground streams in cave dark zones. Decreased dissolved oxygen content in the streams, resulting from land development activities that can cause faster surface runoff, also may affect the amphipod.